Biofilms are associations of microorganisms that develop on a surface. These represent a severe problem as they provide a microenvironment which contains excreted enzymes and other factors, allowing the bacteria to evade host immune responses, including antibodies and cellular immune responses. Further, biofilms can be extremely resistant to removal and disinfection and can act to exclude antibiotics.
Biofilms may involve an aggregation of a single bacterial species or may include more than one species of bacteria. Usually the bacteria are embedded in a layer of extracellular polymers in the form of a matrix.
Bacterial biofilm development on a surface is a process involving (i) exposure of the surface to planktonic bacterial cells; (ii) a two stage process of attachment of the bacteria to the surface; this involves a first stage of initial weak reversible attachment of the bacteria to the surface followed by a second stage of strong irreversible attachment to the surface; (iii) microcolony formation, which results from further growth and development of attached bacteria and includes bacterial translocation across the surface; (iv) macrocolony development, which involves the microcolony increasing in size to result in an organised structure with a distinct architecture; (v) dispersal of bacteria from the mature biofilm.
Hospital acquired infections are a major public health challenge throughout the world. It is estimated that 80% of the infections acquired in hospitals involve biofilms, within which bacteria show up to 1000 times higher resistance to antibiotic treatment and the host immune system when compared to their planktonic counterparts.
Advances in medical devices such as catheters, vascular access devices, peripheral lines, intravenous sites, drains, gastric feeding tubes, trachea tubes, stents, guidewires, pacemakers, and other implantable devices have enormously benefited the diagnostic and therapeutic practices in medical care. However, bacterial infections are becoming one of the most common and serious complications related to the use of implanted medical devices. For example, urinary-tract infection frequently occurs in patients with catheters in place for extended periods of time. Bacterial attachment can be mediated by the mineralisation of salt components within urine, as well as by the effects of non-mineral components, such as creatinine and urea, which can affect polymer surfaces and promote bacterial attachment.
Known strategies for reducing biofilm associated infections focus on the modification of existing materials used to manufacture indwelling medical devices by the introduction of antimicrobial compounds, such as antibiotics. These treatments will generally involve: 1) adsorption of an antimicrobial agent to the surface of the medical device; 2) incorporation of an antimicrobial agent into a polymer coating that is applied on the surface of the medical device; or 3) compounding an antimicrobial agent into the bulk material that is used to make the medical device.
These approaches are therefore based on the leaching of the active antimicrobial agent, which may be an antibiotic or a metal ion. The antimicrobial efficacy is therefore dependent on the loading of the active antimicrobial agent within the material and the rate of its release from the surface.
It is often very difficult to control the release rate and maintain a constant level of concentration at the surface, as the release rate depends on many factors, such as actual concentration, solubility, and ability to diffuse, and these may also change over the timescale during which the medical device is used.
Therefore, a simple and effective method to create a surface with intrinsic resistance against bacterial attachment and biofilm formation is needed.